EVIDENCE FOR IN-VIVO BUT NOT IN-VITRO EXPRESSION OF A BORRELIA-BURGDORFERI OUTER-SURFACE-PROTEIN-F (OSPF) HOMOLOG

Protein export signals from the low-passage 297 strain of Borrelia bur gdorferi were cloned as fusions with an Escherichia coil alkaline phos phatase (PhoA) reporter lacking a signal sequence. One PhoA(+) clone ( BbK2.10-PhoA) was derived from a borrelial lipoprotein, Although the p olypeptide encoded by the full-length bbk2.10 gene had 76% similarity and 56% identity to outer surface protein F (OspF) from B. burgdorferi strain N40, antibodies directed against recombinant forms of the two proteins revealed that they were not cross-reactive, The nucleotide se quences of bbk2.10 and ospF from the N40 and 297 strains, respectively , were determined to confirm that the N40 and 297 strains each contain ed both genes, Southern blot analysis revealed that bbk2.10 is a singl e-copy gene and that the B. burgdorferi strain 297 and N40 genomes app eared to contain one other gene more closely related to ospF than bbk2 .10. It was particularly noteworthy that ospF, but not bbk2.10 was exp ressed in vitro while B. burgdorferi-infected mice generated antibodie s reactive with both lipoproteins, To help confirm that the BbK2.10-re active antibodies produced by the B. burgdorferi-infected mice were sp ecific for that protein, a second gene, bbk2.11, which hybridized with the ospF probe was cloned; the corresponding polypeptide reacted stro ngly with OspF antisera but failed to react with BbK2.10-specific anti sera, Taken together, these data demonstrate that BbK2.10, BbK2.11, an d OspF comprise a B. burgdorferi lipoprotein family and that at least one member (BbK2.10) appears to be expressed only during infection.